<div dir="ltr">On Tue, Aug 27, 2013 at 8:30 PM, Stephen P. Villano <span dir="ltr"><<a href="mailto:stephen.p.villano@gmail.com" target="_blank">stephen.p.villano@gmail.com</a>></span> wrote:<br><div class="gmail_extra">
<div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
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That sounds like one of the filters used back before Comcast
switched to digital. We used to have stacks of them in series, each
filter for each premium channel.<br>
Comcast installers frequently have a bad habit of leaving that junk
behind.<br></div></blockquote><div><br></div><div>Those would be notch filters (they attenuated the premium channel</div><div>frequencies, or the TV frequencies when you only had a cable modem,</div><div>or....)</div>
<div><br></div><div>In any case, in today's cable plant, almost all of those filters are badness,</div><div>as Comcast moves channels around various frequencies, eventually they</div><div>may move something to where the notch filter is/was, and the signal is</div>
<div>too low to be useful.</div><div><br></div><div>Since you mentioned the problem comes and goes, you may have a</div><div>RF leakage issue (and it may be in your wiring, or the outside plant).</div><div>This can be a common problem where the MSO decides to use the</div>
<div>frequencies in the FM band. FM signal comes in, and generates</div><div>"random" noise that results in bad pixelation. And while if the MSO</div><div>has extra bandwidth, there is a tendency to avoid the FM band for</div>
<div>precisely this problem, Comcast is known to use that band (I had</div><div>a hardline broken at a pedestal near me, which resulted in bad</div><div>pixelation for the channels that shared the FM band; the QAM</div><div>
constallation was the classic one for that case; it could have been</div><div>used in the tutorial).</div><div><br></div><div>Before spending any more time try to rework your cabling, call Comcast</div><div>and request the removal of the notch filters, and have them check the</div>
<div>signal levels at your demark, and the noise levels across the spectrum</div><div>to insure there is no leakage. In most cases, for the appointment, the</div><div>best thing to do is to say some channels do not work, and the picture</div>
<div>either freezes, or breaks up. When the tech gets there, the first thing</div><div>they will likely do is remove the notch filters and check the levels</div><div>(because that is the first thing you check).</div><div>
<br></div><div>Gary</div></div></div></div>